Work machine boom assemblies serve a variety of functions such as, digging ditches, loading work trucks, and laying pipe. In order to carry out these functions, the boom assembly must be capable of swinging from side-to-side by rotating the boom about a pivotal connection to the frame. A pair of hydraulic cylinders having one end connected to the boom assembly and the other end connected to the frame of the work machine aide in rotating the boom assembly by extending one cylinder while the other retracts.
When an operator swings the boom assembly quickly and the stop command is given, the swing valve closes and the boom assembly rapidly decelerates. As the boom assembly approaches zero angular velocity, the remaining energy in the swing system is in the form of potential energy stored in the oil and kinetic energy in the swinging boom assembly. The kinetic energy in the swinging boom assembly bounces off the potential energy in the oil and spikes the pressure in the swing system. The pressure spike is enough to blow the relief valve and let oil escape the swing system. Cavitation occurs from the oil-starved swing system, resulting in the boom assembly bouncing from side to side until the energy is dissipated. This is known in the industry as “swing wag” and is undesirable due to pressure spikes in the system, resulting in damage to the hydraulic system and leading to pre-mature life or failure.
Typically, a charge valve or similar device may be used to control “swing wag”. One known “swing wag” control apparatus is found in U.S. Pat. No. 4,757,685, issued to Jerry J. Burckhartzmeyer on Jul. 19, 1988. Burckhartzmeyer discloses a hydraulic control circuit, which utilizes the pressurized fluid from the main supply conduit upstream of the directional control valve to super charge the makeup valves when the directional control valve is in the neutral position. By supercharging the makeup valves, any fluid lost from the associated circuit is immediately replenished, thereby avoiding or minimizing the creation of voids in the system.
The present invention is directed to overcoming one or more of the problems set forth above.